However, with the method disclosed in Japanese Laid-Open Patent Publications Nos. 2003-17054, H6-342657 and H10-270025 in which a baked lithium-containing composite oxide is washed with water, an exchange reaction between Li+ ions and H+ ions is likely to occur between the lithium-containing composite oxide and water. Such an exchange reaction can also occur between water that remains before a dehydration process performed after water-washing and the lithium-containing composite oxide. Li+ ions leached into water cause lithium hydroxide to be newly deposited. Furthermore, such lithium hydroxide reacts with a small amount of carbon dioxide present in the air to generate lithium carbonate. That is, lithium hydroxide and lithium carbonate are regenerated when a lithium-containing composite oxide is washed with water, and there is a limit to the removal of such by-products.
A ketone, such as acetone, as disclosed in Japanese Laid-Open Patent Publication No. 2001-332261 can suppress the exchange reaction between Li+ ions and H+ ions because it does not have an active methylene group. However, such a ketone as a solvent does not easily dissolve lithium hydroxide and lithium carbonate, so there is a limit to its washing effect when used singly to wash a lithium-containing composite oxide.
In view of the above problems, it is an object of the present invention to provide a method for producing a lithium-containing composite oxide wherein the inclusion of lithium hydroxide and lithium carbonate is suppressed to a high degree, and a non-aqueous secondary battery wherein the inclusion of lithium hydroxide and lithium carbonate is suppressed, and battery characteristics and reliability are improved.